using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using Expression = Microsoft.Expression.Interactivity;
using System.Linq;
using System.Windows.Data;
using System.Collections.Generic;
using System.Reflection;

namespace MikesDragDropBits
{
  public class DraggableBehavior : Expression.Behavior<FrameworkElement>
  {
    public DraggableBehavior()
    {
    }
    public string PropertyPath { get; set; }

    protected override void OnAttached()
    {
      base.OnAttached();
      this.AssociatedObject.MouseLeftButtonDown += OnMouseDown;
      this.AssociatedObject.MouseLeftButtonUp += OnMouseUp;
      this.AssociatedObject.MouseMove += OnMouseMove;     
    }
    protected override void OnDetaching()
    {
      base.OnDetaching();
      this.AssociatedObject.MouseLeftButtonDown -= OnMouseDown;
      this.AssociatedObject.MouseLeftButtonUp -= OnMouseUp;
      this.AssociatedObject.MouseMove -= OnMouseMove;
    }
    void OnMouseMove(object sender, MouseEventArgs e)
    {
      if (isDragging)
      {
        if (injectedUI == null)
        {
          Point localPoint = e.GetPosition(this.AssociatedObject);
          Point globalPoint = e.GetPosition(Application.Current.RootVisual);
          capturePoint = globalPoint;
          globalPoint.X -= localPoint.X;
          globalPoint.Y -= localPoint.Y;
          injectedUI = new DragDropUIInjector(this.AssociatedObject, globalPoint);
          injectedUI.InjectUI();
        }
        else
        {
          Point currentPoint = e.GetPosition(Application.Current.RootVisual);
          injectedUI.ApplyDelta(currentPoint.X - capturePoint.X,
            currentPoint.Y - capturePoint.Y);
          capturePoint = currentPoint;
        }
      }
    }
    void OnMouseUp(object sender, MouseButtonEventArgs e)
    {
      this.AssociatedObject.ReleaseMouseCapture();
      isDragging = false;

      if (injectedUI != null)
      {
        injectedUI.RemoveUI();
        injectedUI = null;
        HitTestAndInvokeTriggers(e.GetPosition(Application.Current.RootVisual));
      }
    }
    void HitTestAndInvokeTriggers(Point p)
    {
      object dataObject = GetDataObject();

      foreach (DropTrigger trigger in GetDropTriggersOfFirstElement(p))
      {
        trigger.InvokeActions(dataObject);
      }
    }
    object GetDataObject()
    {
      object dataObject = this.AssociatedObject;

      if (!string.IsNullOrEmpty(this.PropertyPath))
      {
        dataObject = null;

        Type t = this.AssociatedObject.GetType();

        PropertyInfo propertyInfo = t.GetProperty(this.PropertyPath,
          BindingFlags.Public | BindingFlags.Instance);

        if (propertyInfo != null)
        {
          dataObject = propertyInfo.GetValue(this.AssociatedObject, null);
        }
      }
      return (dataObject);
    }
    static IEnumerable<DropTrigger> GetDropTriggersOfFirstElement(Point p)
    {
      var elements = VisualTreeHelper.FindElementsInHostCoordinates(p,
        Application.Current.RootVisual);  

      if (elements != null)
      {
        foreach (var item in elements)
        {
          var triggers = Expression.Interaction.GetTriggers(item);

          if ((triggers != null) && (triggers.Count > 0))
          {
            foreach (Expression.TriggerBase trigger in triggers)
            {
              if (trigger is DropTrigger)
              {
                yield return (DropTrigger)trigger;                
              }
            }
            break;
          }
        }
      }
    }
    void OnMouseDown(object sender, MouseButtonEventArgs e)
    {
      if (!isDragging)
      {
        isDragging = true;
        this.AssociatedObject.CaptureMouse();
      }
    }
    bool isDragging;
    DragDropUIInjector injectedUI;
    Point capturePoint;
  }
}